The present invention relates to glass products in the form of filaments, fibers, hollow spheres, or foamed glass, and suitable for incorporation into light weight concrete. The glass products serve as reinforcements for cement, mortar, concrete or other cementitious materials.
It is well known that cement, mortar and concrete can be improved to withstand tension, impact, and abrasion by the addition of glass fibers. The use of hollow glass spheres or foamed glass as additives to light-weight concrete instead of polystyrene or other synthetic resin foams has the advantage of increased compressive strength in the absence of any water absorption by the latter materials. However, fibers or hollow spheres made of conventional glasses are not generally recommended for the long term reinforcement of concrete or cementitious products because the pH-value of cementitious products, e.g., Portland cement, attacks and substantially weakens said glass fibers and spheres whereby long term reinforcement of cementitious products is not possible.
In order to remedy this situation, the prior art has tried a number of potential solutions. One is to reduce the high pH value with atmospheric carbon dioxide (aeroconcrete) or to introduce carbon dioxide into compacted concrete. This is not satisfactory because the glasses may be utilized only in porous concrete and the process, when used with compacted concrete, is too complicated.
Secondly, it has been proposed to coat fiberglass filaments with alkali-resistant synthetic resins. This has not been satisfactory because of the difficulty of obtaining a completely dense coating on the glasses and the poor adhesion of coated fiberglass filaments to a cement matrix.
It has also been proposed to use highly alkali-resistant glass fibers of spheres. This procedure does not completely eliminate the corrosion of the glass caused by the cement but merely delays this process. Moreover, it also has the disadvantage of resulting in poor adhesion to a cementitious matrix.
Another proposal is to use fibers of alkali-free glass containing a quantity of zinc (see West German Pat. No. 2,129,016). However, this process has the disadvantage that relatively high temperatures are needed for extruding fibers of this type.